1. Field of the Invention
The present invention relates generally to gastroesophageal reflux diagnostic systems, and more particularly to automated system for processing impedance and pH signals from an esophageal monitoring device to locate bolus entry and exit points on an impedance waveform and to locate retrograde bolus movement episodes across impedance channel waveforms.
2. Description of the Background
Gastrointestinal reflux is the movement of liquids, which may, but do not necessarily, include stomach acids, upwardly in the esophagus, i.e., away from the stomach instead of toward the stomach. The esophagus, which extends from a person's or animal's pharynx to the stomach, normally functions to transport food and liquids downwardly from the pharynx to the stomach during a swallow. During a normal swallow, a peristaltic wave (i.e., a contraction of the muscles of the esophagus) begins at the upper end of the esophagus and moves progressively downward in the esophagus and works to push the food or liquid downwardly to the Lower Esophageal Sphincter (LES), which opens and allows the food or liquid to enter the stomach. The LES, which is a circular or ring-like muscle structure, normally prevents the contents of the stomach from re-entering the esophagus. Therefore, in a normal swallow, the esophageal muscles and the LES work in conjunction with each other to transport liquid or food to the stomach and to prevent retrograde movement of the food or liquid in the opposite direction.
Gastrointestinal reflux, or Gastroesophageal reflux disease (GERD), is an abnormal esophageal condition or function in which a portion of the stomach contents passes in a reverse direction through the LES and moves at least some distance upwardly into the esophagus in a retrograde motion. In persons with GERD, the LES muscle may be weak or may relax inappropriately with exposure to fatty and spicy foods, certain types of medications, tight clothing, smoking, drinking alcohol, vigorous exercise, or changes in body position. The reflux can cause problems, such as heartburn-like pain symptoms, chest pain similar to cardiac problems, aggravated asthma symptoms, hoarseness, sinus problems, snoring problems, and other respiratory problems. Severe or prolonged acid reflux can cause inflammation (esophagitis) and can ultimately damage the lining of the esophagus. Reflux is usually not noticeable or harmful during the day, since the esophagus is protected during waking hours by swallowing, by the flow of saliva, and by gravity (assuming the sufferer is standing or sitting up). However, at night, these protective mechanisms are less effective. Consequently, nighttime acid reflux is more likely to remain in the esophagus longer and can cause greater damage.
A normal course of treatment for non-critical reflux is typically the administration of acid-reducing or acid-blocking medications. However, serious and/or long-term gastrointestinal reflux can often necessitate surgery to the LES or to the stomach. Therefore, it is desirable in all cases to be able to detect, measure, and diagnose any abnormal operations of the esophagus in order to prevent or treat the reflux.
One fairly common method of detecting the occurrence of gastrointestinal reflux has been to insert a probe with a pH-sensitive billet into the esophagus of a subject to measure acid or pH levels. For example, one or more antimony billets have been used to detect hydrochloric acid (HCl) as a marker for acid reflux. When the probe in the esophagus detects a drop in pH levels, it is assumed that gastric contents containing HCl have entered the esophagus from the stomach. Consequently, the occurrence of a pH value below about 4.0 is commonly held to indicate a reflux episode. The value of 4.0 pH is commonly used because the esophagus has a typical pH of approximately 6.0 and the stomach has a typical pH of approximately 4.0. The value of 4.0 is commonly held to be the lowest pH level tolerable in the esophagus without causing caustic damage to the esophageal lining.
One drawback of that pH-detecting approach is that acid control medication defeats the ability to detect acid reflux. The HCI acid may not be sufficiently present to be used as a marker for reflux episodes. Another drawback of this approach is that it does not show the operational dynamics of the esophagus, i.e., it does not show bolus movement. (The word “bolus” is used herein as a convenient term to denote any quantity of solid and/or liquid material moving through the esophagus in either direction and is not necessarily limited to a small, round mass.) Consequently, this prior art approach cannot determine the underlying cause of the reflux. In addition, this approach may not be able to continuously measure acid levels in a patient over a significant period of time. Furthermore, it may not show the extent or duration of a reflux occurrence, as the prior art approach is incapable of detecting the reflux of relatively non-acidic stomach fluids, i.e., a “non-acid” reflux.
A more recent development in esophageal monitoring has included the use of a probe to measure electric impedance in the esophagus, such as the probe described in the U.S. Pat. No. 5,109,870 issued to J. Silny et al., which is incorporated herein by reference. Essentially, such impedance probes can sense electric impedances and changes in electric impedances at one or more locations in the esophagus above the LES, including such changes in impedance caused by reflux of stomach contents into the esophagus.
Changes in pH and/or impedance from such esophageal measurements are typically presented as raw numbers or line graphs that show values taken over time. Therefore, a physician or other medical personnel has to interpret the data, i.e., numbers or values from the graphs, in order to obtain meaningful information, such as occurrences of reflux episodes and start and stop times of such episodes. Such interpretations are difficult and time consuming. It is even more difficult if the analyzing person has to correlate multiple data readings for a patient, and it is not unusual for such manual analysis of typical 24-hour gastroesophageal reflux monitoring studies to require up to 4 hours of an experienced clinician's time. This time requirement to discern and extract meaningful information from such pH and/or impedance measurements is significant enough that it is a substantial impediment to use such esophageal impedance data beyond academic interest and research settings. Also, the mental challenge of interpreting impedance waveforms for retrograde bolus movement episodes is enough so that mental fatigue can cause human scoring to degrade over the course of the study.
Therefore, there remains a need for improvements in the detection and analysis of esophageal reflux from impedance and/or pH measurements in the esophagus.